1. Yes. You can also reference
https://www.visajourney.com/guides/us-naturalization/
2. I'm currently going through the N-400 online form.
https://my.uscis.gov/citizenship/what_to_expect
I recommend completing the online form yourself first before determining if you need a lawyer.
3. You can travel while waiting for the interview with the proper documents (passport, green card, etc.). Just make sure you have someone catch the USCIS notification mails so that you can return for the biometrics, interview, appointments, etc.